joker

(noun) a person who enjoys telling or playing jokes. Synonyms: jokester.

(noun) a person who does something thoughtless or annoying. Synonyms: turkey. Example: "Some joker is blocking the driveway."

(noun) an inconspicuous clause in a document or bill that affects its meaning in a way that is not immediately apparent. Example: "When i demanded my money he showed me the joker in the contract."

(noun) a playing card that is usually printed with a picture of a jester.